Nitrogen-doped carbon nanofiber decorated LiFePO<Subscript>4</Subscript> composites with superior performance for lithium-ion batteries

Nitrogen-doped carbon nanofiber (NCNF) decorated LiFePO₄ (LFP) composites are synthesized via an in situ hydrothermal growth method. Electrochemical performance results show that the embedded NCNF can improve electron and ion transfer, thereby resulting in excellent cycling performance. The as-prepared LFP and NCNF composites exhibit excellent electrochemical properties with discharge capacities of 188.9 mAh g^?1 (at 0.2 C) maintained at 167.9 mAh g^?1 even after 200 charge/discharge cycles. The electrode also presents a good rate capability of 10 C and a reversible specific capacity as high as 95.7 mAh g^?1. LFP composites are a potential alternative high-performing anode material for lithium ion batteries.     

Preparation and comparative structural properties of porous SnO2 microrods and submicrorods

A facile two-step approach has been used for the synthesis of porous SnO₂ rods: the initial room-temperature precipitation of precursor SnC₂O₄ and its subsequent thermal decomposition at 550 °C. Both the as-obtained porous SnO₂ microrods (length ～10.0?±?3.5 μm, diameter ～1.1?±?0.4 μm) and submicrorods (length ～5.8?±?1.9 μm, diameter ～0.4?±?0.1 μm) are the crystalline mixtures of major tetragonal and minor orthorhombic crystal phases, showing a tetragonal fraction of 84.7 and 87.0 %, respectively. When applied as a lithium-ion battery anode, the porous submicrorods (specific surface area ～13.6 m² g^?1) can deliver an initial discharge capacity of 1,730.7 mAh g^?1 with a high coulombic efficiency of 61.6 % and show the 50th discharge capacity of 662.8 mAh g^?1 at 160 mA g^?1 within a narrow potential range of 10.0 mV to 2.0 V. Similarly, even the anode of porous microrods (specific surface area ～11.8 m² g^?1) can still exhibit an initial discharge capacity of 1,661.1 mAh g^?1 at 160 mA g^?1 with a coulombic efficiency of 60.9 %. Regardless of the polymorphic nature, the acquired porosity may only alleviate the huge volume change of anodes for the first cycle; thus, the structural parameters of average size and specific surface area can be feasibly associated with the enhanced lithium storage capability. Anyway, these indicate a facile oxalate precursor method for the controlling synthesis and high performance of rodlike SnO₂ for lithium-ion batteries.     

Growth of FePO<Subscript>4</Subscript> nanoparticles on graphene oxide sheets for synthesis of LiFePO<Subscript>4</Subscript>/graphene

FePO₄·xH₂O/graphene oxide (FePO₄·xH₂O/GO) composites were prepared by a facile chemical precipitation method. Using the as-prepared FePO₄·xH₂O/GO and LiOH·H₂O as precursors and followed by carbothermal reduction, LiFePO₄/graphene composites were obtained. Scanning electron microscope (SEM) images indicated that the graphene had very good dispersity and uniformly attached to the LiFePO₄ particles. The conductive framework of graphene improved the electrochemical properties of the composites. The composites deliver high initial discharge capacity of 163.4 mAh g^?1 as well as outstanding rate performance.     

Flower-like MoS<Subscript>2</Subscript> supported on three-dimensional graphene aerogels as high-performance anode materials for sodium-ion batteries

Flower-like MoS₂ supported on three-dimensional graphene aerogel (MoS₂/GA) composite has been prepared by a facile hydrothermal method followed by subsequent heat-treatment process. Each of MoS₂ microflowers is surrounded by the three-dimensional graphene nanosheets. The MoS₂/GA composite is applied as an anode material of sodium-ion batteries (SIBs) and it exhibits high initial discharge/charge capacities of 562.7 and 460 mAh g^?1 at a current density of 0.1 A g^?1 and good cycling performance (348.6 mAh g^?1 after 30 cycles at 0.1 A g^?1). The good Na⁺ storage properties of the MoS₂/GA composite could be attributed to the unique structure which flower-like MoS₂ are homogeneously and tightly decorated on the surface of three-dimensional graphene aerogel. Our results demonstrate that as-prepared MoS₂/GA composite has a great potential prospect as anodes for SIBs.     

Three-dimensional nitrogen-doped graphene/sulfur composite for lithium-sulfur battery

A three-dimensional nitrogen-doped graphene/sulfur composite (NGS3) was synthesized by a simple hydrothermal method using urea as the nitrogen source and subsequent thermal treatment. The structure and electrochemical performance of the prepared nitrogen-doped graphene/sulfur composite (NGS3) were confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Energy dispersive spectroscopy mapping (EDS), and galvanostatic charge/discharge measurements. SEM and EDS mapping show that NGS3 exhibits a porous structure with uniform distribution of sulfur. Compared with the graphene/sulfur composite (NGS1), NGS3 delivers an outstanding rate capability with 1501, 1278, 1136, and 1024 mAh g^?1 at 200, 400, 800, and 1000 mA g^?1, respectively, and the cycle stability of NGS3 is also wonderful, a reversible discharge capacity of 1330 mAh g^?1 is obtained after 80 cycles under the current rate of 200 mA g^?1. The wonderful electrochemical performance could be attributed to the special three-dimensional conductive structure with the help of nitrogen atom.     

Si/polyaniline-based porous carbon composites with an enhanced electrochemical performance as anode materials for Li-ion batteries

Silicon/polyaniline-based porous carbon (Si/PANI-AC) composites have been prepared by a three-step method: coating polyaniline on Si particles using in situ polymerization, carbonizing, and further activating by steam. The morphology and structure of Si/PANI-AC composites have been characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectra, respectively. The content and pore structure of the carbon coating layer in Si/PANI-AC have been measured by thermogravimetric analysis and N₂ adsorption-desorption isotherm, respectively. The results indicate some micropores about 1~2 nm in the carbon layer appear during activation and that crystal structure and morphology of Si particles can be retained during preparation. Si/PANI-AC composites exhibit high discharge capacity about 1000 mAh g^?1 at 1.5 A g^?1; moreover, when the current density returns to 0.2 A g^?1, the discharge capacity is still 1692 mAh g^?1 and remains 1453 mAh g^?1 after 70 cycles. The results indicate that the porous carbon coating layer in composites plays an important role in the improvement of the electrochemical performance of pure Si.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> quantum dots on 3D-framed graphene aerogel as an advanced anode material in lithium-ion batteries

Three-dimensional fabricated Fe₃O₄ quantum dots/graphene aerogel materials (Fe₃O₄ QDs/GA) were obtained from a facile hydrothermal strategy, followed by a subsequently heat treatment process. The Fe₃O₄ QDs (2–5 nm) are anchored tightly and dispersed uniformly on the surface of three-dimensional GA. The as-prepared anode materials exhibit a high reversible capacity of 1078 mAh g^?1 at a current density of 100 mA g^?1 after 70 cycles in lithium-ion batteries (LIBs) system. Moreover, the rate capacity still remains 536 mAh g^?1 at 1000 mA g^?1. The enhanced electrochemical performance is attributed to that the GA not only acts as a three-dimensional electronic conductive matrix for the fast transportation of Li⁺ and electrons, but also provides with double protection against the aggregation and pulverization of Fe₃O₄ QDs during cycling. Apparently, the synergistic effects of the three-dimensional GA and the quantum dots are fully utilized. Therefore, the Fe₃O₄ QDs/GA composites are promising materials as advanced anode materials for LIBs.     

Advanced LiTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C anode by incorporation of carbon nanotubes for aqueous lithium-ion batteries

Inferior rate capability is a big challenge for LiTi₂(PO₄)₃ anode for aqueous lithium-ion batteries. Herein, to address such issue, we synthesized a high-performance LiTi₂(PO₄)₃/carbon/carbon nanotube (LTP/C/CNT) composite by virtue of high-quality carbon coating and incorporation of good conductive network. The as-prepared LTP/C/CNT composite exhibits excellent rate performance with discharge capacity of 80.1 and 59.1 mAh g^?1 at 10 C and 20 C (based on the mass of anode, 1 C = 150 mA g^?1), much larger than that of the LTP/C composite (53.4 mAh g^?1 at 10 C, and 31.7 mAh g^?1 at 20 C). LTP/C/CNT also demonstrates outstanding cycling stability with capacity retention of 83.3 % after 1000 cycles at 5 C, superior to LTP/C without incorporation of CNTs (60.1 %). As verified, the excellent electrochemical performance of the LTP/C/CNT composite is attributed to the enhanced electrical conductivity, rapid charge transfer, and Li-ion diffusion because of the incorporation of CNTs.     

Influence of graphene coating on supercapacitive behavior of sandwich-like N- and O-enriched porous carbon/graphene composites in aqueous and organic electrolytes

Polyacrylonitrile nanofiber cloth coated with graphene oxide was carbonized and activated to fabricate nitrogen- and oxygen-enriched porous carbon/graphene (NAC@Gr) sandwich-like composites. The influence of graphene coating on the microstructure, surface composition, and supercapacitive performance of the as-prepared composites was investigated. The results indicated that significantly enhanced energy storage capability can be achieved due to the high specific surface area, optimized pore structure, and surface functionality. The composites show both high gravimetric and volumetric specific capacitances, for example, 380 F g^?1 (178 F cm^?3) at 0.1 A g^?1 in 6 M KOH and 228 F g^?1 (125 F cm^?3) at 1 A g^?1 in 1 M TEABF₄/AN electrolyte. The assembled symmetric supercapacitors exhibit high energy density, high power density, excellent cycling stability, and high-rate performance.     

Simple microwave synthesis and improved electrochemical performance of Nb-doped MnO<Subscript>2</Subscript>/reduced graphene oxide composite as anode material for lithium-ion batteries

Niobium-doped MnO₂/reduced graphene oxide (Nb-MnO₂/RGO) composite has been successfully synthesized via a simple microwave radiation method. The samples were systematically studied by X-ray diffraction (XRD), thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and electrochemical measurements. As the anode material for lithium-ion batteries, the Nb-MnO₂/RGO (molar ratio of Mn/Nb?=?50:1) (NMG50) showed an outstanding reversible discharge capacity of 556.6 mAh g^?1 after 50 cycles with a capacity retention of 77% at a charge-discharge rate of 0.1 A g^?1 and the reversible discharge capacity can still retain 223.3 mAh g^?1 at a current of 1 A g^?1, which is much higher than those for Nb-MnO₂/RGO (molar ratio of Mn/Nb?=?10:1) (NMG10) and undoped MnO₂/RGO (MG). The improved electrochemical performance could be attributed to the proper amount of Nb doping, which could enhance both the conductivity and the structure stability of MnO₂.     

NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> polyhedra with controllable particle size as high-performance anode for lithium-ion battery

Different particle sizes of dodecahedron precursors are synthesized by controlling the polarity of the solution. Through the results of scanning electron microscope (SEM) images, it can be found that different particle sizes of precursors present obvious edge angles and their morphology can be well retained after annealing. X-ray diffraction (XRD) measurements suggest that the annealed polyhedral products are pure single-phase NiCo₂O₄. When tested as lithium-ion battery anode, 0.5 μm NiCo₂O₄ polyhedra exhibits a specific capacity of 1050 mAh g^?1 at 0.1 C at the 60th cycle, which was higher than theoretical capacity of single metal oxide (NiO 718 mAh g^?1 and Co₃O₄ 890 mAh g^?1). It also exhibits the highest rate capability with an average discharge capacity of 890, 700, 490, 330, and 300 mAh g^?1 at 0.5, 2, 4, 8, and 10 C, respectively. Those advantages are attributed to that small-sized particle with great surface areas decrease the actual current density at the surface and inner of the prepared electrode.     

Preparation and characterization of Li1.2Ni0.13Co0.13Mn0.54O2 cathode materials for lithium-ion battery

Lithium-rich cathode materials Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ with (sample SF) and without (sample SP) formamide was synthesized by a spray-dry method. The crystalline structure and particle morphology of as-prepared materials were characterized by X-ray diffraction and scanning electron microscope. The specific surface area (SSA) of the Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ prepared from different routes was determined by a five-point Brunauer–Emmett–Teller (BET) method using N₂ as absorbate gas. Being compared with the material synthesized without spray-drying process (sample CP), sample SP has much higher SSA. The additive formamide is helpful to form regular and solid precursor particles in spray-drying process, which results in a slightly aggregation of grains and reduction of SSA for sample SF. The electrochemical activities of the materials are closely related to their morphology and SSA. In the voltage range of 2–4.8 V at 25 °C, sample SP present a discharge capacity of 257 mAh g^?1 at 0.1 C rate and 170 mAh g^?1 at 1 C rate. The sample CP delivered only 136 mAh g^?1 when discharged at 1 C rate. The elevated specific capacity and rate capability are attributed to smaller primary particle and higher SSA. Both cycle performance and rate capability of Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ were improved when formamide was used in spray-dry process. Discharge capacity of SF is 140.5 mAh g^?1 at 2 C rate, and that of SP is 132.3 mAh g^?1. Overlarge SSA of SP may provoke serious side reaction, so that its electrochemical performance was deteriorated.     

N-doped graphene/Bi nanocomposite with excellent electrochemical properties for lithium–ion batteries

N-doped graphene/Bi nanocomposite was prepared via a two-step method, combining the gas/liquid interface reaction with the rapid heat treatment method. The as-prepared sample was characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), and elemental analyzer. The XRD, FESEM, XPS, and elemental analysis results confirm the successful synthesis of N-doped graphene/Bi nanocomposite. As a result, the prepared N-doped graphene/Bi nanocomposite as an anode material for lithium-ion batteries delivers excellent electrochemical performance. A high lithium storage capacity of about 522 mAh g^?1 in the voltage range of 0.01–3.5 V is obtained. After 50 cycles at different current densities from 50 to 1000 mA g^?1, the specific capacity can still remain 386 mAh g^?1. Even at the high current density of 1000 mA g^?1, the N-doped graphene/Bi nanocomposite can still deliver a specific capacity of 218 mAh g^?1. The excellent electrochemical performance of the N-doped graphene/Bi nanocomposite is supposed to benefit from the high electronic conductivity of nitrogen-doped graphene and the synergistic effect of bismuth nanoparticles and nitrogen-doped graphene.     

Scalable synthesis and superior performance of TiO<Subscript>2</Subscript>-reduced graphene oxide composite anode for sodium-ion batteries

TiO₂-reduced graphene oxide (RGO) composite was synthesized via a sol-gel process and investigated as an anode material for sodium-ion batteries (SIBs). A remarkable improvement in sodium ion storage with a reversible capacity of 227 mAh g^?1 after 50 cycles at 50 mA g^?1 is achieved, compared to that (33 mAh g^?1) for TiO₂. The enhanced electrochemical performance of TiO₂-RGO composite is attributed to the larger specific surface area and better electrical conductivity of TiO₂-RGO composite. The excellent performance of TiO₂-RGO composite enables it a potential electrode material for SIBs.     

The intercalation/deintercalation kinetic studies on the structure-integrated cathode material 0.5Li2MnO3 0.5LiNi0.5Mn0.5O2

A cathode material, 0.5Li₂MnO₃ 0.5LiNi_0.5Mn_0.5O₂, was prepared by citric acid-assisted sol–gel method and its electrochemical performance was investigated. It delivered a charge capacity of 270 mAh g^?1 and a discharge capacity of 189 mAh g^?1 in the first cycle. With the increase of current density from 14 to 28 mA g^?1, the discharge capacity dropped severely to 130 mA g^?1. Obviously, the rate capability of the material was inferior to most of the oxide cathode materials. The diffusion coefficient of this material was calculated to be 6.04?×?10^?12 cm² s^?1 from the results of cyclic voltammetry measurements. Moreover, diffusion coefficients between 3.13?×?10^?12 and 1.22?×?10^?10 cm² s^?1 in the voltage range of 3.8–4.7 V were obtained by capacity intermittent titration technique. This, together with the localized Li₂MnO₃ domains in the crystal structure, may validate the poor rate capability.     

Preparation of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> hollow microsphere/graphene/carbon nanotube flexible film as a binder-free anode material for lithium-ion batteries

A flexible Co₃O₄ hollow microsphere/graphene/carbon nanotube hybrid film is successfully prepared through a facile filtration strategy and a subsequent thermally treated process. The composition, morphology, and structure of the as-prepared film are characterized by X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. Based on the morphology characterizations on the hybrid film, the Co₃O₄ hollow microspheres are uniformly and closely attached on three-dimensional (3D) graphene/carbon nanotubes (GR/CNTs) network, which decreases the agglomeration of Co₃O₄ microspheres effectively. In this hybrid film, the 3D GR/CNT network which enhances conductance as well as prevents aggregation is a benefit to help Co₃O₄ to exert its lithium storage capabilities sufficiently. When used as a binder-free anode material for lithium-ion batteries, the hybrid film delivers excellent electrochemical properties involving reversible capacity (863 mAh g^?1 at a current density of 100 mA g^?1) and rate performance (185 mAh g^?1 at a current density of 1600 mA g^?1).     

Influence of post-calcination treatment on the spinel lithium titanium oxide anode material for lithium ion batteries

The influence of post-calcination treatment on spinel Li₄Ti₅O₁₂ anode material is extensively studied combining with a ball-milling-assisted rheological phase reaction method. The post-calcinated Li₄Ti₅O₁₂ shows a well distribution with expanded gaps between particles, which are beneficial for lithium ion mobility. Electrochemical results exhibit that the post-calcinated Li₄Ti₅O₁₂ delivers an improved specific capacity and rate capability. A high discharge capacity of 172.9 mAh g^?1 and a reversible charge capacity of 171.1 mAh g^?1 can be achieved at 1 C rate, which are very close to its theoretical capacity (175 mAh g^?1). Even at the rate of 20 C, the post-calcinated Li₄Ti₅O₁₂ still delivers a quite high charge capacity of 124.5 mAh g^?1 after 50 cycles, which is much improved over that (43.9 mAh g^?1) of the pure Li₄Ti₅O₁₂ without post-calcination treatment. This excellent electrochemical performance should be ascribed to the post-calcination process, which can greatly improve the lithium ion diffusion coefficient and further enhance the electrochemical kinetics significantly.     

The centrifugally constructed and thermally activated three-dimensional graphene toward a binder-free highly performed anode of the lithium-ion battery

A binder-free three-dimensional porous interconnected graphene (a-3DrGO@NF) was centrifugally constructed and KOH-activated at 800 °C, leading a mechanically strong and pore-developed anode candidate for lithium ion batteries (LIBs). The unique approach of the integration of the mechanical construction and thermal activation demonstrated favorable frameworks to facilitate the stable and fast migrations of both ion and electron during the galvanostatic charge/discharge process, thus significantly improving its durability and electrochemical performance compared to those without the activated and thermal treatment. The a-3DrGO@NF LIBs showed a highly reversible capacity of 1250 mAh g^?1 at a current density of 0.1 A g^?1 after 50 cycles without degradation relative to the first cycle. More importantly, the a-3DrGO@NF LIBs exhibited excellent large current discharge property and cyclic stability of 965 mAh g^?1 in its first cycle and 545 mAh g^?1 after 150 cycles at a current density of 4 A g^?1. Furthermore, it can be quickly charged and discharged in a very short time of 92 s together with high-rate capability of 256 mAh g^?1 after 200 cycles at 10 A g^?1. At both lower and higher its current density as to 10 A g^?1, the coulombic efficiency was close to 100% and showed the reliability of a-3DrGO@NF LIBs.     

Graphene and polydopamine double-wrapped porous carbon-sulfur cathode materials for lithium-sulfur batteries with high capacity and cycling stability

Rechargeable lithium-sulfur batteries are deemed to be a promising energy supply to next-generation high energy power system, yet dissolution of lithium polysulfides in the electrolyte leads to poor cycling performance. Here, we report an approach to assemble graphene and polydopamine double-wrapped porous carbon/sulfur (GN-PD-PC-S) for lithium-sulfur batteries. Remarkably, the double-wrapping graphene and polydopamine further help confine the sulfur and polysulfides inside the mesopores and micropores of porous carbon. Moreover, the hierarchical porous structures provide a conductive network for electron transfer and facilitate the effective accommodation of the volume change of sulfur. The GN-PD-PC-S cathode presents an excellent cycling stability of 821 mAh g^?1 after 100 cycles, with a favorable high-rate capability of 496 mAh g^?1 at a current density of 2 A g^?1. Our results indicate the importance of chemically synergistic effect of polymer and carbon in the electrode system for achieving high-performance electrodes in rechargeable lithium-sulfur batteries.     

ZnO nanoparticles anchored on nitrogen and sulfur co-doped graphene sheets for lithium-ion batteries applications

Herein, we demonstrate a facile one-step hydrothermal synthesis route to anchor ZnO nanoparticles on nitrogen and sulfur co-doped graphene sheets. The detailed material and electrochemical characterization have been carried out to demonstrate the potential of novel ZnO/NSG nanocomposite in Li-ion battery (LIBs) applications. The structure and morphology of nanocomposite were assessed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as-synthesized ZnO/NSG nanocomposite has been studied as anode material in LIBs and delivered a high initial discharge capacity of 1723 mAh g^?1, at the current density of 200 mA g^?1. After 100 cycles, the ZnO/NSG nanocomposites demonstrated a high reversible capacity of 720 mAh g^?1 and coulombic efficiency of 99.8%, which can be attributed to the porous three-dimensional network, constructed by ZnO nanoparticles and nitrogen and sulfur co-doped graphene. Moreover, the designed nanocomposite has shown excellent rate capability and lower charge transfer resistance. These results are promising and encourage further research in the area of ZnO-based anodes for next-generation LIBs.